﻿334 
  Fenner 
  — 
  Stability 
  Relations 
  of 
  Silica 
  Minerals. 
  

  

  elusions 
  be 
  arrived 
  at 
  without 
  supplementary 
  evidence. 
  The 
  

   explanations 
  suggested 
  for 
  these 
  debatable 
  problems 
  must 
  be 
  

   looked 
  upon 
  merely 
  as 
  contributions 
  toward 
  a 
  final 
  solution 
  of 
  

   the 
  theoretical 
  questions 
  involved. 
  

  

  After 
  the 
  investigation 
  had 
  been 
  under 
  way 
  for 
  some 
  time 
  

   a 
  preliminary 
  paper 
  was 
  published.* 
  In 
  this 
  a 
  brief 
  outline 
  

   was 
  given 
  of 
  the 
  chief 
  results 
  obtained 
  up 
  to 
  that 
  time. 
  In 
  

   the 
  present 
  paper 
  it 
  has 
  seemed 
  desirable 
  to 
  present 
  the 
  results 
  

   as 
  a 
  consistent 
  whole, 
  so 
  far 
  as 
  possible, 
  and 
  in 
  order 
  to 
  do 
  

   this 
  all 
  results 
  of 
  importance 
  will 
  be 
  given 
  and 
  their 
  relations 
  

   discussed 
  without 
  much 
  regard 
  to 
  the 
  previous 
  publication. 
  

  

  Determination 
  of 
  the 
  Inversion 
  Points 
  between 
  Quartz 
  and 
  

   Tridymite 
  and 
  between 
  Tridymite 
  and 
  Cristobalite. 
  

  

  As 
  previous 
  work 
  had 
  demonstrated 
  that 
  the 
  above 
  inversions 
  

   take 
  place 
  very 
  slowly, 
  and 
  that 
  the 
  minerals 
  may 
  be 
  heated 
  at 
  

   high 
  temperatures 
  and 
  for 
  long 
  periods 
  with 
  no 
  indication 
  of 
  

   inversion 
  or 
  with 
  only 
  partial 
  inversion 
  as 
  the 
  result, 
  it 
  was 
  

   realized 
  at 
  the 
  outset 
  that 
  it 
  was 
  necessary 
  to 
  employ 
  a 
  flux 
  or. 
  

   catalytic 
  agent 
  of 
  some 
  sort 
  to 
  hasten 
  the 
  process. 
  This 
  should 
  

   be 
  such 
  a 
  material 
  as 
  would 
  melt 
  at 
  a 
  comparatively 
  low 
  tem- 
  

   perature 
  and 
  would 
  not 
  be 
  volatilized 
  to 
  a 
  serious 
  degree 
  at 
  

   high 
  temperatures. 
  It 
  should, 
  moreover, 
  not 
  dissolve 
  silica 
  in 
  

   large 
  quantity 
  or 
  enter 
  into 
  solid 
  solution 
  with 
  any 
  of 
  the 
  silica 
  

   minerals. 
  A 
  number 
  of 
  reagents 
  were 
  tried 
  at 
  various 
  times, 
  

   such 
  as 
  potassium 
  and 
  lithium 
  chlorides, 
  boric 
  acid, 
  and 
  salt 
  of 
  

   phosphorus, 
  but 
  the 
  one 
  which 
  best 
  fulfilled 
  the 
  requirements 
  

   was 
  found 
  to 
  be 
  crystallized 
  sodium 
  tungstate 
  (Na 
  2 
  W0 
  4 
  , 
  2H 
  2 
  0). 
  

   This 
  possessed 
  the 
  added 
  advantage 
  that 
  it 
  could 
  be 
  removed 
  

   by 
  simple 
  washing 
  with 
  water. 
  The 
  only 
  difficulty 
  found 
  was 
  

   that 
  at 
  high 
  temperatures 
  (1400° 
  and 
  over) 
  it 
  dissolves 
  a 
  con- 
  

   siderable 
  quantity 
  of 
  silica, 
  and 
  if 
  much 
  is 
  used 
  nothing 
  but 
  a 
  

   glass 
  results. 
  This 
  difficulty 
  was 
  easily 
  overcome 
  by 
  using 
  a 
  

   small 
  quantity. 
  

  

  For 
  reactions 
  at 
  a 
  high 
  temperature, 
  that 
  is, 
  in 
  the 
  neighbor- 
  

   hood 
  of 
  the 
  tridymite 
  -cristobalite 
  inversion 
  -point, 
  sodium- 
  

   potassium 
  silicate 
  may 
  likewise 
  be 
  employed. 
  It 
  offers 
  no 
  spe- 
  

   cial 
  advantages 
  over 
  sodic 
  tungstate, 
  except 
  that 
  it 
  may 
  be 
  

   regarded 
  as 
  more 
  similar 
  in 
  its 
  nature 
  to 
  a 
  magmatic 
  melt. 
  

  

  In 
  establishing 
  the 
  inversion 
  points, 
  the 
  method 
  of 
  procedure 
  

   was 
  simple 
  in 
  principle 
  but 
  rather 
  tedious 
  in 
  its 
  application 
  

   because 
  of 
  the 
  slowness 
  with 
  which 
  equilibrium 
  is 
  established. 
  

   A 
  charge 
  was 
  first 
  prepared 
  by 
  melting 
  sodic 
  tungstate 
  in 
  a 
  

   small 
  platinum 
  crucible 
  over 
  a 
  Bunsen 
  flame 
  and 
  adding 
  the 
  

   respective 
  form 
  of 
  silica 
  and 
  mixing 
  with 
  a 
  platinum 
  stirrer. 
  

   The 
  crucible, 
  to 
  which 
  a 
  short 
  wire 
  had 
  been 
  fused 
  on 
  each 
  

  

  * 
  The 
  Various 
  Forms 
  of 
  Silica 
  and 
  their 
  Mutual 
  Relations, 
  C. 
  N. 
  Fenner, 
  

   J. 
  Wash. 
  Acad. 
  Sci., 
  ii, 
  471-480, 
  1912. 
  

  

  